1. Field of the Invention
The present invention relates to a structure of an air blowing device, and particularly to a ventilating fan in which a sirocco fan is provided.
2. Description of the Related Art
A known ventilating fan 100 is shown in FIG. 1. A sirocco fan 120 is disposed in a box-shaped body 110. An air is suctioned through an air inlet 111 at a bottom of the body 110 and discharged to the outdoors through an air outlet 112 on a side of the body 110. Furthermore, a metal adapter 1500 is disposed at the air outlet 112 on the side of the body 110 so as to discharge the air to the outdoors through the air outlet 112. The metal adapter 1500 is connected with a duct (not shown) communicating with the outdoors.
The air outlet 112 of the sirocco fan 120 has a square shape. However, one end of the duct communicating with the outdoors has a round shape. Meanwhile, an area of the air outlet 112 of the sirocco fan 120 is larger than a section area of the duct. Therefore, a wind path area is necessary to be reduced at the metal adapter 1500. As shown in FIG. 1, the square air outlet is evenly reduced to form a round shape. That is to say, opposite edges of the square of the air outlet 112 are symmetrically reduced from the outer circumference towards the center.
The above air blowing device of the prior art has the following problems: the air blown by the sirocco fan 120 is difficult to be smoothly transformed since the square shape of the air outlet 112 is different from the round shape of the duct. That is to say, the air blown by the sirocco fan 120 is not uniform and thus prone to generate turbulence although the air outlet is evenly reduced. The ventilating fan cannot ensure amount of the blown air due to this turbulence. Thus, a large sirocco fan is required to ensure the amount of the blown air. However, the large sirocco fan will generate stronger noise.
FIG. 5 shows a structurally schematic view of a metal adapter of a known ventilating fan. The metal adapter 1500 of the ventilating fan comprises an air guiding structure 1100 and a shutter 1200 mounted inside the air guiding structure 1100. The air guiding structure 1100 is divided into two parts: an air inlet 1110 and an air outlet 1120. The air inlet 1110 is connected to the casing (not shown) mounted with the fan and the air outlet 1120 is connected to the duct (not shown) communicating with outdoors. The air inlet 1110 has a square shape and the air outlet 1120 has a round shape. The square air inlet 1110 is gradually reduced while extending towards the round air outlet 1120. A sidewall 1130 forms a smooth transition between the air inlet 1110 and the air outlet 1120 so as to form a structure like funnel. The shutter 1200 entirely has a shape formed of a plane 1210 and a folded edge 1220. The shutter 1200 is mounted at a position close to outdoor side in the round air outlet 1120 via seven components such as glue sheaths 1230, rivets 1240, a rubber buckle 1250 and so on.
It is apparent from the above description that the known metal adapter 1500 is composed of the shutter 1200, the air guiding structure 1100, the two sheaths 1230, the two rivets 1240 and the rubber buckle 1250.
The inventors of the present invention have found that the above adapter structure of the prior art has the following disadvantages or problems:
The adapter structure cannot be smoothly connected with the casing provided with the fan since the area of the air inlet 1110 is too large. That is to say, the air outlet of the fan is sharply enlarged at the air inlet 1110. In this way, when wind generated by the fan is blown towards the air inlet 1110, the wind will collide with the sidewall 1130 of the air inlet so as to generate turbulence and the amount of the wind is thus reduced while noise is generated;
Since the shutter 1200 entirely has the shape formed of the plane and the folded edge, a slit is formed between the shutter 1200 and the round air outlet 1120, thereby causing poor air tightness (prone to reverse airflow into the indoor from the outdoor through the duct);
In addition, it is shown from FIG. 6 that the shutter 1200 is mounted at a position close to the outdoor side in the round air outlet 1120. Therefore, a screw 1300 may contact with the shutter 1200 and the shutter 1200 thus cannot be opened when an operator fixes the outdoor connecting duct 1210 to the air outlet by the screw 1300.